The overarching goal of this research project is to determine the long-term health effects of methamphetamine (hereafter "meth") use within an existing cohort of men who have sex with men (MSM) participating in the Multicenter AIDS Cohort Study (MACS). More specifically, this proposal focuses on the stimulant abuse effects on health issues that occur at the intersection of mental health, drug abuse and HIV infection. Meth use among MSM has become an increasingly important behavioral risk factor associated with co-occurring epidemics of HIV and other biopsychosocial health problems. However, meth research among MSM has generally been limited to cross-sectional or relatively short-term cohort studies. Therefore our understandings of the factors that predict initiation of meth use, the specific mechanisms of how meth use results in long term health consequences, whether stimulant drug use has unique health outcomes among minority MSM or whether meth use results in poorer health outcomes among HIV+ MSM remain poorly defined. These gaps inhibit our ability to respond effectively to the health consequences of meth use among MSM. The Specific Aims of this proposal are to identify the precursors of meth use and/or abuse among MSM, to identify the development of co-morbidities among MSM meth users, to test whether substance use drives HIV risk among minority men and to test whether meth use hastens disease progression among HIV-positive men in the HAART era. The use of an existing cohort will allow us to rigorously examine the long-term health effects of meth use in ways that are not only cost-effective in terms of financial expenditures but also in terms of the even more important economic dimension of timeliness.